A Failure Of Faith

Et cum venisset ad turbam, accessit ad eum homo genibus provolutus, dicens, Domine, miserere filio meo. Reverso ad turbas Domino, a patre genibus advoluto puer offertur daemoniacus, frequenter et in aquam decidens et in ignem, cui curationem afferre discipuli non potuerint. Objurgatis his, et increpato daemone, sanus puer factus est. Crediderant quidem Apostoli: nondum tamen erant perfectae fidei. Nam Domino in monte demorante, et ipsis cum turba residentibus, quidam tepor eorum fidem relaxaverat; atque idcicro ait: Generatio incredibilis et perversa, quousque ero vobiscum? Quia, absente se, antiquae infidelitatis consuetudo subrepserat. Docet igitur, eos nihil salutis afferre posse, qui medio Evangeliorum et iterati adventus tempore, a fide tamen Domino absente decesserint. Sanctus Hilarius Pictaviensis, In Evangelium Matthaei Commentarius, Cap XVII Source: Migne PL 9.1015-1016

And when He had come to the crowd, a man approached Him, who falling on his knees, said, 'Lord, have pity on my Son.' 1 As the Lord returned to the crowd, the father, kneeling, presented his child, a demoniac, who often threw himself into the water and into fire. The disciples were unable to obtain a cure for him. After scolding them and rebuking the demon, the boy was healed. Though the Apostles believed, their faith was not yet perfect. While the Lord delayed on the mountain, they were sitting with the crowd and a kind of torpor had weakened their faith, and therefore He said to them, 'Unbelieving and perverse generation, how long will I be with you?'  2 In His absence, their old habit of unbelief had come back to them. Thus He taught them that they would not obtain salvation who, during the time intervening between the Gospels and the Second Coming, abandoned their faith with the Lord absent.   Saint Hilary of Poitiers, from the Commentary On The Gospel of Saint Matthew, Chapter 17 1 Mt 17.15 2 Mt 17.17